Communication method of a vehicular mobile terminal, a macro base station, a neighbor micro base station, and a serving micro base station in a multi-cell group

ABSTRACT

A communication method of a serving micro base station is provided. The method includes a handover of a vehicular mobile terminal based on uplink broadcast information including a unique access code allocated to the vehicular mobile terminal within a multi-cell group. The multi-cell group includes a macro base station and a plurality of micro base stations within a cell coverage of the macro base station. The handover is performed based on a determined preparation level of the handover that is based on the uplink broadcast information.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2010-0038819, filed on Apr. 27, 2010, in theKorean Intellectual Property Office, the entire disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND

1. Field

The following description relates to a communication method of a basestation and a vehicular mobile terminal, and more particularly, to acommunication method of a serving micro base station, a neighbor microbase station, a macro base station, and a vehicular mobile terminal.

2. Description of Related Art

In a mobile communication system, a terminal may be mobile. Because ofthis mobility, when the terminal moves near the edge of or beyond theservice coverage of a base station serving the terminal, a handover ofthe terminal to a new base station is needed in order to maintainservice. In a wireless communication system, determining whether toperform a handover is based on various qualities, for example, thequality of a downlink channel between a terminal to be handed over and atarget base station.

A base station serving a terminal to be handed over may request theterminal to measure qualities of a neighbor base station and a wirelesslink, and report about the measurement results to the base station. Theserving base station may request the new target base station for ahandover based on reported values of the qualities of a wirelesschannel, and the target base station may provide a response to therequest.

When receiving an acceptance message of the handover from the targetbase station, the serving base station may transmit a message toinstruct performance of the handover to the terminal, and the terminalmay send a response message to the base station in service indicatingthat the handover is to be performed.

SUMMARY

In one general aspect, there is provided a communication method of aserving micro base station that is serving a vehicular mobile terminal,the method comprising identifying a unique access code allocated to thevehicular mobile terminal in a multi-cell group, the multi-cell groupcomprising a macro base station and a plurality of micro base stationsthat are within a cell coverage of the macro base station, receivinguplink broadcast information including the unique access code from thevehicular mobile terminal, and performing a handover of the vehicularmobile terminal based on the uplink broadcast information.

The unique access code may be allocated to the vehicular mobile terminalbased on a mobility of the vehicular mobile terminal.

The method may further comprise collecting information about a receivingstate of the uplink broadcast information of a neighbor micro basestation from the neighbor micro base station in the multi-cell group.

The method may further comprise determining a preparation level of ahandover associated with a level of an operation used for the servingmicro base station and a neighbor micro base station to perform thehandover.

The determining of the preparation level of the handover may comprisedetermining a preparation level of the handover based on the uplinkbroadcast information received by the serving micro base station anduplink broadcast information received by the neighbor micro basestation.

The determining of the preparation level of the handover may comprisedetermining a preparation level of the handover based on at least one ofa mobility of the vehicular mobile terminal, an estimated cell residencetime of the vehicular mobile terminal, a backhaul environment betweenthe serving micro base station and the neighbor micro base station, anamount of data used by the vehicular mobile terminal, a load of theserving micro base station, and a load of the neighbor micro basestation.

The method may further comprise reporting about the determinedpreparation level of the handover to the neighbor micro base station.

The determining of the preparation level of the handover may comprisedetermining a preparation level of the handover to be at one of aplurality of levels including at least one of a preregistration, anuplink synchronization setup, an acceptance of a handover andperformance of the handover, a joint interference control for thevehicular mobile terminal, a joint processing on the vehicular mobileterminal, and a cell merger.

The method may further comprise estimating a cell residence time of thevehicular mobile terminal based on the uplink broadcast informationreceived from the serving micro base station.

The vehicular mobile terminal may comprise at least one of a femto basestation, a moving relay, and a mobile terminal.

In another aspect, there is provided a communication method of aneighbor micro base station, the method comprising identifying a uniqueaccess code allocated to a vehicular mobile terminal in a multi-cellgroup, the multi-cell group comprising a macro base station and aplurality of micro base stations within a cell coverage of the macrobase station, overhearing uplink broadcast information including theunique access code from the vehicular mobile terminal, and reportinginformation about a receiving state of the uplink broadcast informationto a serving micro base station that is serving the vehicular mobileterminal.

The reporting information about the receiving state of the uplinkbroadcast information may comprise reporting the information about thereceiving state of the uplink broadcast information in order todetermine a preparation level of a handover associated with a level ofan operation used for the serving micro base station and a neighbormicro base station to perform the handover.

The method may further comprise identifying the preparation level of thehandover based on a report of the serving micro base station.

The method may further comprise performing the handover of the vehicularmobile terminal based on the preparation level of the handover.

The identifying of the unique access code may comprise receivinginformation about a channel allocated for the unique access code fromthe macro base station.

The method may further comprise performing coordinated communicationwith the serving micro base station based on the determination of theserving micro base station, when the preparation level of the handoveris determined to be a level including at least one of joint interferencecontrol for the vehicular mobile terminal and joint processing on thevehicular mobile terminal.

The method may further comprise estimating an uplink timing offset orestimating a quality of service (QoS) of the vehicular mobile terminal,based on the uplink broadcast information.

In another aspect, there is provided a communication method of avehicular mobile terminal, the method comprising identifying a uniqueaccess code allocated to the vehicular mobile terminal in a multi-cellgroup, the multi-cell group comprising a macro base station and aplurality of micro base stations within a cell coverage of the macrobase station, and broadcasting uplink broadcast information includingthe unique access code to the plurality of micro base stations.

The method may further comprise receiving information about a channelallocated for the unique access code from the macro base station,wherein the broadcasting of the uplink broadcast information comprisesbroadcasting the uplink broadcast information using the channelallocated for the unique access code.

In another aspect, there is provided a communication method of a macrobase station, the method comprising identifying a mobility of avehicular mobile terminal in a multi-cell group, the multi-cellcomprising the macro base station and a plurality of micro base stationswithin a cell coverage of the macro base station, allocating a uniqueaccess code and a channel for the unique access code to the vehicularmobile terminal based on the mobility of the vehicular mobile terminal,and reporting about the unique access code and the channel for theunique access code to the plurality of micro base stations.

The method may further comprise regaining the unique access code and thechannel for the unique access code based on the mobility of thevehicular mobile terminal.

The method may further comprise forwarding data about the vehicularmobile terminal from a serving micro base station to a neighbor microbase station based on a renewed data forwarding path, when a preparationlevel of a handover associated with a level of an operation used for theserving micro base station and the neighbor micro base station toperform the handover uses data forwarding.

The method may further comprise forwarding data about the vehicularmobile terminal to a neighbor micro base station when a preparationlevel of a handover associated with a level of an operation used for aserving micro base station and the neighbor micro base station toperform the handover uses cooperation between the serving micro basestation and the neighbor micro base station.

In another aspect, there is provided a computer-readable storage mediumhaving stored therein program instructions to cause a processor toimplement a communication method of a serving micro base station that isserving a vehicular mobile terminal, the method comprising identifying aunique access code allocated to the vehicular mobile terminal in amulti-cell group, the multi-cell group comprising a macro base stationand a plurality of micro base stations that are within a cell coverageof the macro base station, receiving uplink broadcast informationincluding the unique access code from the vehicular mobile terminal, andperforming a handover of the vehicular mobile terminal based on theuplink broadcast information.

Other features and aspects may be apparent from the followingdescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a multi-cell group.

FIG. 2 is a diagram illustrating an example of a vehicular mobileterminal communicating with a macro base station and a vehicular mobileterminal communicating with a micro base station using differentchannels in the multi-cell group.

FIGS. 3A and 3B are diagrams illustrating examples of a process ofperforming a handover based on uplink broadcast information in amulti-cell group.

FIG. 4 is a diagram illustrating an example of a switch from a generalhandover scheme based on a measurement report of a downlink signal to ahandover scheme based on uplink broadcast information.

FIG. 5 is a diagram illustrating an example of a preparation level of ahandover that is determined differently in each cell of a multi-cellgroup.

FIG. 6 is a flowchart illustrating an example of a communication methodof a serving micro base station in a multi-cell group.

FIG. 7 is a flowchart illustrating an example of a communication methodof a neighbor micro base station in a multi-cell group.

FIG. 8 is a flowchart illustrating an example of a communication methodof a vehicular mobile terminal in a multi-cell group.

FIG. 9 is a flowchart illustrating an example of a communication methodof a macro base station in a multi-cell group.

Throughout the drawings and the description, unless otherwise described,the same drawing reference numerals should be understood to refer to thesame elements, features, and structures. The relative size and depictionof these elements may be exaggerated for clarity, illustration, andconvenience.

DESCRIPTION

The following description is provided to assist the reader in gaining acomprehensive understanding of the methods, apparatuses, and/or systemsdescribed herein. Accordingly, various changes, modifications, andequivalents of the methods, apparatuses, and/or systems described hereinmay be suggested to those of ordinary skill in the art. Also,description of well-known functions and constructions may be omitted forincreased clarity and conciseness.

In the following description, a vehicular mobile terminal may include amobile terminal which is installed in a vehicle and a mobile terminalwhich is transportable by a user. The term “mobile” may refer to anobject in motion or to an object at rest that is capable of being setinto motion.

FIG. 1 illustrates an example of a multi-cell group.

Referring to FIG. 1, the multi-cell group includes a macro cell 100, amacro base station 110, a plurality of micro cells 120 within a cellcoverage of the macro base station 110, a plurality of micro basestations 130 within the cell coverage of the macro base station 110, anda vehicular mobile terminal 140.

For example, the plurality of micro cells 120 may be fully or partiallyincluded in the coverage area of the macro cell 100, and the micro cells120 may each include a respective micro base station 130.

The plurality of micro base stations 130 may include a serving microbase station that is currently serving the vehicular mobile terminal 140and the neighbor micro base stations that may operate as a serving microbase station when a handover is performed.

For example, the macro base station 110 may allocate a unique accesscode and a channel for the unique access code to the vehicular mobileterminal 140 that is travelling within the macro cell 100 based on amobility of the vehicular mobile terminal 140.

The unique access code and the channel for the unique access code may beallocated to the vehicular mobile terminal 140 based on the mobility ofthe vehicular mobile terminal 140, for example, the unique access codeand the channel for the unique access code may be allocated to thevehicular mobile terminal 140 based on a predetermined speed and thelike.

For example, the mobility of the vehicular mobile terminal 140 mayinclude a traveling speed, a traveling direction, an estimated cellresidence time, a traveling path, and the like, of the vehicular mobileterminal 140.

In this example, the estimated cell residence time may be changed basedon a radius of the cell coverage. The mobility may also include anintensity of a signal received from the vehicular mobile terminal 140 tothe serving micro base station and the neighbor micro base stations.

As an example, the unique access code allocated to the vehicular mobileterminal 140 may be available for a channel measurement of the vehicularmobile terminal 140, uplink synchronization, a joint cell formation, ahandover determination, and the like. The unique access code and thechannel for the unique access code allocated to the vehicular mobileterminal 140 may be maintained within the coverage of the same macrobase station 110. For example, the unique access code and the channelfor the unique access code allocated to the vehicular mobile terminal140 may be renewed or maintained when a handover is performed betweenthe macro cell 100 and another macro cell.

The vehicular mobile terminal 140 has the unique access code within themulti-cell such as the micro cells 120 or the macro cell 100 andvehicular mobile terminal 140 broadcasts uplink broadcast informationincluding the unique access code to the micro base stations 130 in themacro cell 100.

The micro base stations 130 may receive the uplink broadcast informationincluding the unique access code from the vehicular mobile terminal 140.For example, the serving micro base station may collect uplink broadcastinformation or information about the uplink broadcast information, forexample, uplink reception power, received from a neighbor micro basestation. The serving micro base station may use the collectedinformation to perform a handover.

As an example, the vehicular mobile terminal 140 may include at leastone of a femto base station, a moving relay, a mobile terminal, and thelike.

FIG. 2 illustrates an example of a vehicular mobile terminalcommunicating with a macro base station and a vehicular mobile terminalcommunicating with a micro base station using different channels in amulti-cell group.

FIG. 2 illustrates an example in which a vehicular mobile terminal 240that communicates with a macro base station 210 and a vehicular mobileterminal 245 that communicates with a micro base station 230 coexistusing a same-frequency channel. In this example, different channels maybe allocated to a unique access code of the vehicular mobile terminal240 in the macro cell 200 and a unique access code of the vehicularmobile terminal 245 in the micro cell 220, respectively.

For example, different channels may be allocated to prevent the uniqueaccess codes transmitted by the vehicular mobile terminals 245 in themicro cell 220 from going undetected, for example, due to a power of theunique access code transmitted by the vehicular mobile terminal 240 witha high power communicating with the macro base station 210 positioned ona cell boundary. As an example, a power level of the unique access codetransmitted by each of the vehicular mobile terminals 240 and 245 may beset by the macro base station 210 or the micro base station 230.

A transmission power of the unique access code transmitted by each ofthe vehicular mobile terminals 245 in the micro cell 220 may bedetermined based on a transmission power offset value of arepresentative vehicular mobile terminal traveling in the cell, shown indotted line.

For example, the transmission power offset value of the representativevehicular mobile terminal traveling in the cell (a vehicular mobileterminal in a dotted line) may be obtained, and the micro base station230 may broadcast the value such that an adjacent vehicular mobileterminal may use the value. For example, the above scheme may be basedon an adjacent vehicular mobile terminal travelling on a road havingsimilar conditions of position and speed, and thus, communication pathsand link qualities may be similar.

FIGS. 3A and 3B illustrate examples of a process of performing ahandover based on uplink broadcast information in a multi-cell group.

Referring to FIGS. 3A and 3B, the multi-cell group includes a vehicularmobile terminal 301, a macro base station 305, and various micro basestations 303, 307, and 309. The macro base station 305 has acorresponding macro cell, and the micro base stations 303, 307, and 309have corresponding micro cells.

When the vehicular mobile terminal 301 within a cell coverage of themacro base station 305 gains initial random access to the macro basestation 305, in 311, the macro base station 305 registers the vehicularmobile terminal 301, for example, through communication with a servingmicro base station 303, in 313. For example, the vehicular mobileterminal 301 may include at least one of a femto base station, a movingrelay, and a mobile terminal.

The macro base station 305 identifies a mobility of the vehicular mobileterminal 301 in the multi-cell group, in 315, and the macro base station305 detects a change in the mobility of the vehicular mobile terminal301, in 317.

For example, the mobility of the vehicular mobile terminal 301 mayinclude a traveling speed, a traveling direction, an estimated cellresidence time, a traveling path, and the like, of the vehicular mobileterminal 301. For example, the estimated cell residence time may bechanged based on a radius of the cell coverage. For example, theestimated cell residence time may be changed based on GPS information ofthe vehicular mobile terminal 301, traveling speed information of thevehicular mobile terminal 301, information about road conditions such aschange time information of a traffic light, and the like. In someembodiments, an intensity of a signal (for example, uplink broadcastinformation) received from the vehicular mobile terminal 301 to theserving micro base station 303 and the neighbor micro base stations 307and 309 may also be represented by a mobility function.

The macro base station 305 allocates a unique access code and a channelfor the unique access code to the vehicular mobile terminal 301, forexample, based on the mobility of the vehicular mobile terminal 301, in319.

The unique access code allocated to the vehicular mobile terminal 301 isidentified by the vehicular mobile terminal 301 in the multi-cell group,the serving micro base station 303 that is providing a communicationservice to the vehicular mobile terminal 301, and the neighbor microbase stations 307 and 309, in 321.

The vehicular mobile terminal 301 broadcasts uplink broadcastinformation including the unique access code to the plurality of microbase stations 303 and 307 within the cell coverage of the macro basestation 305, in 323. For example, the uplink broadcast informationincluding the unique access code broadcasted by the vehicular mobileterminal 301 may only reach the neighbor micro base station 1 307, andmay not reach the micro base station 2 309.

In 323, for example, the neighbor micro base station 1 307 may overhearthe uplink broadcast information including the unique access code fromthe vehicular mobile terminal 301. Accordingly, in 323 the neighbormicro base station 1 307 may report information about a receiving stateof the uplink broadcast information to the serving micro base station303 of the vehicular mobile terminal 301.

For example, the plurality of neighbor micro base stations (here, theneighbor micro base station 1 307) within the cell coverage of the macrobase station 305 may estimate an uplink timing offset or quality ofservice (QoS) of the vehicular mobile terminal 301 based on theoverheard uplink broadcast information including the unique access code.As another example, the serving micro base station 303 and the neighbormicro base stations (here, the neighbor micro base station 1 307) withinthe cell coverage of the macro base station 305 may estimate a cellresidence time of the vehicular mobile terminal 301 based on the uplinkbroadcast information received from the vehicular mobile terminal 301.

To estimate the cell residence time of the vehicular mobile terminal301, the serving micro base station 303 and the neighbor micro basestations (here, the neighbor micro base station 1 307) may use, forexample, GPS information of the vehicular mobile terminal 301, travelingspeed information of the vehicular mobile terminal 301, informationabout road conditions such as change time information of a trafficlight, and the like.

The serving micro base station 303 collects information about thereceiving state of the uplink broadcast information of the neighbormicro base station 1 307 based on the report from the neighbor microbase station 1 307, in 325.

The serving micro base station 303 may determine whether to perform ahandover of the vehicular mobile terminal 301 based on the uplinkbroadcast information. In addition, the serving micro base station 303may determine a preparation level of the handover associated with alevel of an operation used for the serving micro base station 303 andthe neighbor micro base station 1 307 to perform the handover. Forexample, the serving micro base station 303 may determine thepreparation level of the handover based on the uplink broadcastinformation received by the serving micro base station 303 and theuplink broadcast information received by the neighbor micro base station1 307.

The serving micro base station 303 may determine the preparation levelof the handover as one of a plurality of levels, For example, theplurality of the levels may include at least one of a preregistration ofeach of the serving micro base station 303 and the neighbor micro basestation 1 307, an uplink synchronization setup, an acceptance of ahandover and performance of the handover, a joint interference controlfor the vehicular mobile terminal 301, a joint processing on thevehicular mobile terminal 301, a cell merger, and the like.

An example in which the preparation level of the handover is determinedis joint processing on the vehicular mobile terminal 301 in operation327 is described with reference to the examples of FIGS. 3A and 3B.

In this example, the serving micro base station 303 exchanges newtopology information for a joint processing on the vehicular mobileterminal 301 with the neighbor micro base station 1 307, in 329. Forexample, the new topology information may include information used forcommunication with the neighbor micro base station 1 307 based on ajoint processing on the vehicular mobile terminal 301.

The vehicular mobile terminal 301 transmits and receives data for thevehicular mobile terminal 301 in cooperation with the neighbor microbase station 1 307, in 331. The vehicular mobile terminal 301 broadcaststhe uplink broadcast information including the unique access code again,in 333. For example, the uplink broadcast information including theunique access code may be broadcasted to not only the neighbor microbase station 1 307 but also to the neighbor micro base station 2 309 dueto the mobility of the vehicular mobile terminal 301.

The serving micro base station 303 may collect information about areceiving state of the uplink broadcast information from not only theneighbor micro base station 1 307 but also the neighbor micro basestation 2 309, in 335.

The serving micro base station 303 determines the preparation level ofthe handover again based on the collected information in operation 335,and may determine a joint processing on the vehicular mobile terminal301 with the neighbor micro base station 1 307 and the neighbor microbase station 2 309, in 337. The data is then processed in 339.

For example, when the serving micro base station 303 determines a jointprocessing on the vehicular mobile terminal 301, the serving micro basestation 303 may transmit and receive data for the vehicular mobileterminal 301 in cooperation with the neighbor micro base station 1 307and the neighbor micro base station 2 309, in 331. Accordingly, the datamay be joint-processed by the serving micro base station 303 and thevehicular mobile terminal 301 in cooperation with the neighbor microbase station 1 307 and the neighbor micro base station 2 309.

Referring to FIG. 3B, the vehicular mobile terminal 301 continuallybroadcasts the uplink broadcast information according to the mobility ofthe vehicular mobile terminal 301, in 341, and the serving micro basestation collects information of a receiving state of the uplinkbroadcast information from the neighbor micro base stations 307 and 309,in operation 343.

When it is determined that a handover is needed for the vehicular mobileterminal 301, the serving micro base station 303 may determine thepreparation level of the handover to be a handover performance. Forexample, in 345 the serving micro base station 303 may determine ahandover to the neighbor micro base station 1 307 which is a neighbormicro base station that the vehicular mobile terminal 301 isapproaching.

In 345, the serving micro base station 303 may determine the preparationlevel of the handover based on the uplink broadcast information receivedby the serving micro base station 303, and the uplink broadcastinformation and the information about the receiving state of the uplinkbroadcast information received by the neighbor micro base stations 307and 309.

Based on the determining the need for the handover, the micro basestation 303 that was acting as a serving micro base station becomes aneighbor micro base station, and the base station 307 that was acting asa neighbor micro base station becomes a serving micro base station.

After the handover, the vehicular mobile terminal 301 with mobilitycontinually broadcasts the uplink broadcast information, in 347, and thenew serving micro base station 307 collects information about areceiving state of the uplink broadcast information from the neighbormicro base stations 303 and 309, in 349.

The new serving micro base station 307 determines a preparation level ofa handover to be a handover performance to the neighbor micro basestation 2 309 based on the mobility of the vehicular mobile terminal301, in 351.

In 351, for example, the serving micro base station 307 may determinethe preparation level of the handover based on the uplink broadcastinformation received from the vehicular mobile terminal 301, and theuplink broadcast information and the information about the receivingstate of the uplink broadcast information collected from the neighboradjacent micro base stations 303 and 309.

Based on the determination of performance of the handover in 351, theserving micro base station 307 transmits new topology information to thevehicular mobile terminal 301 and the neighbor micro base station 309 tobe a next serving micro base station, in 353. For example, the neighbormicro base station 2 309 may become a serving micro base station basedon the performance of the handover.

The vehicular mobile terminal 301 broadcasts the uplink broadcastinformation including the unique access code based on the mobility, in355.

The serving micro base station 309 receiving the uplink broadcastinformation including the unique access code from the vehicular mobileterminal 301 detects that the vehicular mobile terminal 301 is leavingthe cell coverage of the macro base station 305, in 357.

The macro base station 305 regains the unique access code and thechannel for the unique access code allocated to the vehicular mobileterminal 301 when the vehicular mobile terminal 301 moves beyond thecoverage of the macro cell, in 359.

As described above, the serving micro base station 307 may allocate orregain a unique access code and a channel for the access code to thevehicular mobile terminal 301 instead of the macro base station 305, andmay report about this to the macro base station 305.

The aforementioned handover based on the uplink broadcast informationmay be used along with a general handover scheme, which is describedwith reference to FIG. 4.

FIG. 4 illustrates an example of a switch from a general handover schemebased on a measurement report of a downlink signal and to a handoverscheme based on uplink broadcast information.

Referring to FIG. 4, the multi-cell group includes a vehicular mobileterminal 401 and various micro base stations 403, 405, and 407. Themicro base stations 403, 405, and 407 have corresponding micro cells.

For example, when a vehicular mobile terminal 401 stops or travels at alow speed, a handover may be performed according to a general handoverscheme. In 410, a serving micro base station 403 and a neighbor microbase station 1 405 transmit a preamble and a synchronization channel tothe vehicular mobile terminal 401.

For example, the vehicular mobile terminal 401 measures a preamblesignal or a synchronization signal received through a downlink, andtransmits a measurement report to the serving micro base station 403, in415.

The serving micro base station 403 determines to perform a handoverbased on the report, in 420, and performs the handover, in 425. As aresult of the handover, the base station 403 that was the serving microbase station becomes a neighbor micro base station, and the base station405 that was the neighbor micro base station becomes a serving microbase station.

In an area where the vehicular mobile terminal 401 travels at a highspeed, the serving micro base station 405 may identify the high speedmobility of the vehicular mobile terminal, in 430.

In 435, the serving micro base station 405 allocates a unique accesscode and a channel for the unique access code to the vehicular mobileterminal 401 according to a mobility of the vehicular mobile terminal401.

Subsequently, in operations 440 to 455, a neighbor micro base station 2407 may become a new serving micro base station. Operations 440 to 455are similar to operations 341 to 345 described above with reference toFIGS. 3A and 3B, and thus description thereof will not be repeated.

When serving micro base station detects that the vehicular mobileterminal 401 to which the unique access code is allocated decreases inmobility or has no mobility, in 460, the serving micro base station 407may request the vehicular mobile terminal 401 to return the uniqueaccess code and the channel for the unique access code, in 465.

The serving micro base station 407 regains the unique access code andthe channel for the unique access code from the vehicular mobileterminal 401, in 470.

Accordingly, as described with reference to FIG. 4, a micro base stationmay perform a general handover based on a measurement report of adownlink. In addition, a micro base station may perform a handover basedon uplink broadcast info. The micro base station may switch between ageneral handover and a handover based on uplink broadcast info. Forexample, the micro base station may switch a handover method when ahandover is requested from a mobile terminal, based on the currentmobility of the mobile terminal.

FIG. 5 illustrates an example of a preparation level of a handover thatis determined differently in each cell of a multi-cell group.

Referring to FIG. 5, the multi-cell group includes a base station of amicro cell 1 510, a base station of a micro cell 2 520, a base stationof a micro cell 3 530, and a vehicular mobile terminal 540. In thisexample, the micro cells 510, 520, and 530 are adjacent to each other.

In this example, the backhaul environment of the multi-cell groupincludes a non-data sharing environment such as X2 interface orinternet, and the vehicular mobile terminal 540 has a mobility from themicro cell 1, the micro cell 2, to the micro cell 3. Also in thisexample, the micro base station of the micro cell 1 510 functions as aserving micro base station, the micro base station of the micro cell 2520 is a neighbor micro base station, and the micro base station of themicro cell 3 530 is another neighbor micro base station.

When the vehicular mobile terminal 540 has a low mobility, for example,a low traveling speed of the vehicular mobile terminal 540, the servingmicro base station 510 may determine to perform a handover to themicrocell 2 when determining a preparation level of a handover of thevehicular mobile terminal 540.

For example, the serving micro base station 510 may determine thepreparation level of the handover to perform a joint interferencecontrol for the vehicular mobile terminal 540 with the neighbor microbase station 520.

Accordingly, the neighbor micro base station 520 may accept the handoverof the vehicular mobile terminal 540, may perform an uplinksynchronization process, and may perform a joint interference controlwith the serving micro base station 510.

When the vehicular mobile terminal 540 changes from a low mobility to amedium mobility, for example, a medium traveling speed, it may becomedifficult to share a joint interference control signal because of theincrease in traveling speed. That is, a joint interference controlbetween the serving micro base station 510 and the neighbor micro basestation 520 may be difficult to perform when the vehicular mobileterminal 540 that had a low mobility increases to a medium mobility.

In this example, when the serving micro base station 510 determines thehandover to the micro cell 2 520, the neighbor micro base station 520may accept the handover of the vehicular mobile terminal 540 and performan uplink synchronization process.

When the vehicular mobile terminal 540 has a high mobility, for example,a high traveling speed of the vehicular mobile terminal 540, a handoverto the micro cell 3 may be performed in a short time after the handoverto the micro cell 2. Thus, the neighbor micro base station 530 mayperform a preregistration process and an uplink synchronization processin advance.

For example, the backhaul environment of the multi-cell group may be adata sharing environment such as remote radio head (RRH), and thevehicular mobile terminal 540 may have a mobility from the micro cell 1,the micro cell 2, to the micro cell 3.

When the backhaul environment of the multi-cell group is RRH, datasharing is possible. When the vehicular mobile terminal 540 has a lowmobility, for example, a low traveling speed of the vehicular mobileterminal 540, the serving micro base station 510 may determine ahandover to the micro cell 2. The serving micro base station 510 mayperform a joint interference control during data sharing, for example,joint processing with the neighbor micro base station 520.

The neighbor micro base station 520 may accept the handover of thevehicular mobile terminal 540 and may perform an uplink synchronizationprocess and a joint interference control during data sharing.

The serving micro base station 510 and the neighbor micro base station520 may perform the same preparation level of the handover in thevehicular mobile terminal 540 having medium or high mobility as in thebackhaul environment of a non-data sharing environment.

In this example, the micro cell 3 is not immediately adjacent to themicro cell 1 corresponding to the serving micro base station 510. Whenthe vehicular mobile terminal 540 has a high mobility, the neighbormicro base station 530 corresponding to the micro cell 3, may perform apreregistration process through a backhaul of the preparation level ofthe handover, and may further perform an uplink synchronization process.

As described above, the serving micro base station 510 and the neighbormicro base stations 520 and 530 may receive uplink broadcast informationincluding a unique access code received from the vehicular mobileterminal 540.

For example, the serving micro base station 510 may determine thepreparation level of the handover based on at least one of a mobility ofthe vehicular mobile terminal 540 in the multi-cell group, an estimatedcell residence time of the vehicular mobile terminal 540, a backhaulenvironment between the serving micro base station 510 and the neighbormicro base stations 520 and 530, an amount of data used by the vehicularmobile terminal 540, a load of the serving micro base station 510, aload of the respective neighbor micro base stations 520 and 530, and thelike.

FIG. 6 illustrates an example of a communication method of a servingmicro base station in a multi-cell group.

Referring to FIG. 6, the serving micro base station identifies a uniqueaccess code allocated to a vehicular mobile terminal in the multi-cellgroup, in 610. In this example, the multi-cell group includes at least amacro base station and a plurality of micro base stations within a cellcoverage of the macro base station. In 620, the serving micro basestation receives uplink broadcast information including the uniqueaccess code from the vehicular mobile terminal.

The serving micro base station collects information about a receivingstate of the uplink broadcast information of a neighbor micro basestation from the neighbor micro base station positioned in themulti-cell group, in 630. For example, the information about thereceiving state of the uplink broadcast information may includeinformation useful to determine a preparation level of a handover foreach cell such as the load of each neighbor micro base station,information about wireless conditions, and the like.

The serving micro base station determines whether a handover is neededbased on the uplink broadcast information received by the serving microbase station and the uplink broadcast information received by theneighbor micro base station, in 640. Based on the result of thedetermination in 640, the serving micro base station may determine apreparation level of a handover based on the aforementioned informationwhen the handover is needed, in 650.

The preparation level of the handover determined in 650 may be any oneof a plurality of levels, for example, at least one of apreregistration, an uplink synchronization setup, an acceptance of ahandover and performance of the handover, a joint interference controlfor the vehicular mobile terminal, a joint processing on the vehicularmobile terminal, a cell merger, and the like.

For example, the joint interference control for the vehicular mobileterminal may be used to minimize interference in a channel, for example,frequency and time, which is allocated to the vehicular mobile terminaland being used. The joint interference control may enable coordinatedcommunication by an exchange of control information between the servingmicro base station and neighbor micro base stations.

Further, the joint processing on the vehicular mobile terminal maydenote a shared joint processing and may enable a coordinatedcommunication by sharing of data about the vehicular mobile terminalbetween the serving micro base station and neighbor micro base stations.

For example, the preparation level of the handover may be determined tobe at least one preparation level from a preregistration having a lowpreparation complexity to a cell merger having a high preparationcomplexity. Further, the preparation level of the handover may bedetermined differently in each micro base station in which a handover isperformed.

An example in which the vehicular mobile terminal has a high mobilityand travels from a micro cell 1 to a micro cell 2 as described abovewith reference to FIG. 5 is described herein.

When the serving micro base station determines to perform a handover ofthe vehicular mobile terminal, a preparation level of the handover ofthe serving micro base station may be a performance of the handover, anda preparation level of the handover of a neighbor micro base station 1may be an acceptance of the handover and a performance of an uplinksynchronization process. In addition, a preparation level of thehandover of a neighbor micro base station 2 may be a preregistrationprocess and may further include a performance an uplink synchronizationprocess as necessary.

As described above, for example, the preparation level of the handovermay be determined differently based on a mobility of the vehicularmobile terminal, an estimated cell residence time of the vehicularmobile terminal, a backhaul environment between the serving micro basestation and the neighbor micro base stations, an amount of data used bythe vehicular mobile terminal, a load of the serving micro base station,a load of the neighbor micro base station, a wireless environment, andthe like.

For example, the estimated cell residence time may be determined basedon a size of a cell, a level of an uplink reception signal, a speed ofthe vehicular mobile terminal, a path of the vehicular mobile terminal,and the like.

The serving micro base station reports about the preparation level ofthe handover determined in 650 to the neighbor micro base station, in660. At the same time, the serving micro base station may request ahandover to the neighbor micro base station to perform the handover.

When receiving an acceptance of the handover, for example, anacknowledgement (ACK) signal from a micro base station that requestedthe handover, in 670, the serving micro base station performs thehandover of the vehicular mobile terminal according to the preparationlevel of the handover determined, in 680.

FIG. 7 illustrates an example of a communication method of a neighbormicro base station in a multi-cell group.

Referring to FIG. 7, in 710 the neighbor micro base station identifies aunique access code allocated to a vehicular mobile terminal in themulti-cell group. The multi-cell group includes at least a macro basestation and a plurality of micro base stations within a cell coverage ofthe macro base station.

For example, in 710 the neighbor micro base station may receiveinformation about a channel allocated for the unique access code fromthe macro base station. For example, the information about the channelmay include information about a pattern of the access code and time orfrequency allocated to the access code. The neighbor micro base stationmay estimate an uplink timing offset or QoS of a mobile terminal basedon uplink broadcast information.

The neighbor micro base station overhears the uplink broadcastinformation including the unique access code from the vehicular mobileterminal, in 720.

In 730, the neighbor micro base station reports information about areceiving state of the uplink broadcast information to the serving microbase station of the vehicular mobile terminal.

In 730, the neighbor micro base station may report the information aboutthe receiving state of the uplink broadcast information in order todetermine a preparation level of a handover associated with a level ofan operation used for the serving micro base station and the neighbormicro base station to perform the handover.

The neighbor micro base station may determine whether there is a requestfor a handover from the serving micro base station, in 740. The neighbormicro base station may identify a preparation level of a handover basedon a report by the serving micro base station before and/or afterperforming 740.

For example, when the preparation level of the handover is determined tobe a level including at least one of a joint interference control forthe vehicular mobile terminal and a joint processing on the vehicularmobile terminal, the neighbor micro base station may respond to therequest from the serving micro base station and perform a coordinatedcommunication with the serving micro base station.

When there is a request for a handover from the serving micro basestation in 740, the neighbor micro base station determines whether it ispossible to accept the handover as the preparation level of the handoverreported by the serving micro base station, in 750.

The neighbor micro base station accepts the handover when it is possibleto accept the handover as the preparation level of the handover reportedin 750, and reports about an acceptance of the handover to the servingmicro base station, in 760, for example, by transmitting an ACK.

The neighbor micro base station performs the handover of the vehicularmobile terminal based on the preparation level of the handover agreedwith the serving micro base station, in 770.

FIG. 8 illustrates an example of a communication method of a vehicularmobile terminal in a multi-cell group.

Referring to FIG. 8, in 810 the vehicular mobile terminal in themulti-cell group identifies a unique access code allocated to thevehicular mobile terminal in the multi-cell group. The multi-cell groupincludes a macro base station and a plurality of micro base stationswithin a cell coverage of the macro base station. The unique access codemay be allocated by the macro base station. The vehicular mobileterminal broadcasts uplink broadcast information including the uniqueaccess code to the plurality of micro base stations, in 820.

In 820, the vehicular mobile terminal may receive information about achannel allocated for the unique access code from the macro basestation, and may broadcast the uplink broadcast information using thechannel allocated for the unique access code.

For example, the vehicular mobile terminal may include at least one of afemto base station, a moving relay, and a mobile terminal.

For example, the methods of the serving micro base station and theneighbor micro base station described above with reference to FIGS. 6and 7 may be realized by a moving relay mounted on a vehicle. Forexample, a handover may be performed between a serving moving relay anda neighbor moving relay.

FIG. 9 illustrates an example of a communication method of a macro basestation in a multi-cell group.

Referring to FIG. 9, in 910 the macro base station in the multi-cellgroup identifies a mobility of a vehicular mobile terminal in the cell.The multi-cell group includes at least the macro base station and aplurality of micro base stations within a cell coverage of the macrobase station.

In 920, the macro base station allocates a unique access code and achannel for the unique access code to the vehicular mobile terminalaccording to the mobility of the vehicular mobile terminal.

The unique access code and the channel for the unique access code may beallocated, for example, to the vehicular mobile terminal having amobility of a predetermined speed.

For example, the unique access code may be available for a channelmeasurement of the vehicular mobile terminal, uplink synchronization, ajoint cell formation, and a handover determination.

For example, the mobility of the vehicular mobile terminal may include atraveling speed, a traveling direction, an estimated cell residencetime, and a traveling path of the vehicular mobile terminal. Theestimated cell residence time may be changed on a radius of the cellcoverage or a level of an uplink reception signal.

As another example, the estimated cell residence time may be estimatedusing GPS information of the vehicular mobile terminal, traveling speedinformation of the vehicular mobile terminal, information about roadconditions such as traffic light information, and the like, based onuplink broadcast information including the unique access code receivedfrom a serving micro base station.

The macro base station reports about the unique access code and thechannel for the unique access code allocated to the vehicular mobileterminal, to the plurality of micro base stations, in 930.

For example, the plurality of micro base stations may include theserving micro base station to provide a communication service to thevehicular mobile terminal and a neighbor micro base station adjacent tothe serving micro base station.

The macro base station may regain the unique access code and the channelfor the unique access code based on the mobility of the vehicular mobileterminal.

For example, as described above with reference to FIGS. 3 and 4, themacro base station may regain the unique access code and the channel forthe unique access code allocated to the vehicular mobile terminal whenthe vehicular mobile terminal moves beyond coverage of a macro cell ordecreases in mobility.

The macro base station may forward data about the vehicular mobileterminal from the serving micro base station to one or more neighbormicro base stations according to a renewed data forwarding path when apreparation level of a handover associated with a level of an operationused for the serving micro base station and the neighbor micro basestation to perform the handover uses cooperation between the servingmicro base station and the neighbor micro base station.

In addition, the macro base station may forward the data about thevehicular mobile terminal to a neighbor micro base station when thepreparation level of the handover associated with a level of anoperation used for a serving micro base station and the neighbor microbase station to perform the handover requests cooperation between theserving micro base station and the neighbor micro base station.

As a non-exhaustive illustration only, the terminal device describedherein may refer to mobile devices such as a cellular phone, a personaldigital assistant (PDA), a digital camera, a portable game console, anMP3 player, a portable/personal multimedia player (PMP), a handhelde-book, a portable lab-top personal computer (PC), a global positioningsystem (GPS) navigation, and devices such as a desktop PC, a highdefinition television (HDTV), an optical disc player, a setup box, andthe like, capable of wireless communication or network communicationconsistent with that disclosed herein.

A computing system or a computer may include a microprocessor that iselectrically connected with a bus, a user interface, and a memorycontroller. It may further include a flash memory device. The flashmemory device may store N-bit data via the memory controller. The N-bitdata is processed or will be processed by the microprocessor and N maybe 1 or an integer greater than 1. Where the computing system orcomputer is a mobile apparatus, a battery may be additionally providedto supply operation voltage of the computing system or computer.

It should be apparent to those of ordinary skill in the art that thecomputing system or computer may further include an application chipset,a camera image processor (CIS), a mobile Dynamic Random Access Memory(DRAM), and the like. The memory controller and the flash memory devicemay constitute a solid state drive/disk (SSD) that uses a non-volatilememory to store data.

The processes, functions, methods and/or software described above may berecorded, stored, or fixed in one or more computer-readable storagemedia that includes program instructions to be implemented by a computerto cause a processor to execute or perform the program instructions. Themedia may also include, alone or in combination with the programinstructions, data files, data structures, and the like. Examples ofcomputer-readable storage media include magnetic media such as harddisks, floppy disks, and magnetic tape; optical media such as CD ROMdisks and DVDs; magneto-optical media such as optical disks; andhardware devices that are specially configured to store and performprogram instructions, such as read-only memory (ROM), random accessmemory (RAM), flash memory, and the like. Examples of programinstructions include both machine code, such as produced by a compiler,and files containing higher level code that may be executed by thecomputer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations and methods described above, or vice versa. In addition,a computer-readable storage medium may be distributed among computersystems connected through a network and non-transitory computer-readablecodes or program instructions may be stored and executed in adecentralized manner.

A number of examples have been described above. Nevertheless, it shouldbe understood that various modifications may be made. For example,suitable results may be achieved if the described techniques areperformed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

What is claimed is:
 1. A communication method of a serving micro basestation that is serving a vehicular mobile terminal, the methodcomprising: identifying a unique access code allocated to the vehicularmobile terminal in a multi-cell group comprising a macro base stationand a plurality of micro base stations that are within a cell coverageof the macro base station, the unique access code comprising areturnable identification of the vehicular mobile terminal while thevehicular mobile terminal is within the cell coverage of the macro basestation; receiving uplink broadcast information including the uniqueaccess code from the vehicular mobile terminal; performing a handover ofthe vehicular mobile terminal based on the uplink broadcast information;and regaining the unique access code from the vehicular mobile terminal,in response to the vehicular mobile terminal decreasing in mobility. 2.The method of claim 1, wherein the unique access code is allocated tothe vehicular mobile terminal based on a mobility of the vehicularmobile terminal.
 3. The method of claim 1, further comprising collectinginformation about a receiving state of the uplink broadcast informationof a neighbor micro base station from the neighbor micro base station inthe multi-cell group.
 4. The method of claim 1, further comprisingdetermining a preparation level of a handover associated with a level ofan operation used for the serving micro base station and a neighbormicro base station to perform the handover.
 5. The method of claim 4,wherein the determining of the preparation level of the handovercomprises determining a preparation level of the handover based on theuplink broadcast information received by the serving micro base stationand uplink broadcast information received by the neighbor micro basestation.
 6. The method of claim 4, wherein the determining of thepreparation level of the handover comprises determining a preparationlevel of the handover based on at least one of a mobility of thevehicular mobile terminal, an estimated cell residence time of thevehicular mobile terminal, a backhaul environment between the servingmicro base station and the neighbor micro base station, an amount ofdata used by the vehicular mobile terminal, a load of the serving microbase station, and a load of the neighbor micro base station.
 7. Themethod of claim 4, further comprising reporting about the determinedpreparation level of the handover to the neighbor micro base station. 8.The method of claim 4, wherein the determining of the preparation levelof the handover may comprise determining a preparation level of thehandover to be at one of a plurality of levels including at least one ofa preregistration, an uplink synchronization setup, an acceptance of ahandover and performance of the handover, a joint interference controlfor the vehicular mobile terminal, a joint processing on the vehicularmobile terminal, and a cell merger.
 9. The method of claim 6, furthercomprising estimating a cell residence time of the vehicular mobileterminal based on the uplink broadcast information received from theserving micro base station.
 10. The method of claim 1, wherein thevehicular mobile terminal comprises at least one of a femto basestation, a moving relay, and a mobile terminal.
 11. A communicationmethod of a neighbor micro base station, the method comprising:identifying a unique access code allocated to a vehicular mobileterminal in a multi-cell group comprising a macro base station and aplurality of micro base stations within a cell coverage of the macrobase station, the unique access code comprising a returnableidentification of the vehicular mobile terminal while the vehicularmobile terminal is within the cell coverage of the macro base station;overhearing uplink broadcast information including the unique accesscode from the vehicular mobile terminal; reporting information about areceiving state of the uplink broadcast information to a serving microbase station that is serving the vehicular mobile terminal; andregaining the unique access code from the vehicular mobile terminal, inresponse to the vehicular mobile terminal decreasing in mobility. 12.The method of claim 11, wherein the reporting information about thereceiving state of the uplink broadcast information comprises reportingthe information about the receiving state of the uplink broadcastinformation in order to determine a preparation level of a handoverassociated with a level of an operation used for the serving micro basestation and a neighbor micro base station to perform the handover. 13.The method of claim 12, further comprising identifying the preparationlevel of the handover based on a report of the serving micro basestation.
 14. The method of claim 13, further comprising performing thehandover of the vehicular mobile terminal based on the preparation levelof the handover.
 15. The method of claim 11, wherein the identifying ofthe unique access code comprises receiving information about a channelallocated for the unique access code from the macro base station. 16.The method of claim 13, further comprising performing coordinatedcommunication with the serving micro base station based on thedetermination of the serving micro base station, when the preparationlevel of the handover is determined to be a level including at least oneof joint interference control for the vehicular mobile terminal andjoint processing on the vehicular mobile terminal.
 17. The method ofclaim 12, further comprising estimating an uplink timing offset orestimating a quality of service (QoS) of the vehicular mobile terminal,based on the uplink broadcast information.
 18. A communication method ofa vehicular mobile terminal, the method comprising: identifying a uniqueaccess code allocated to the vehicular mobile terminal in a multi-cellgroup comprising a macro base station and a plurality of micro basestations within a cell coverage of the macro base station, the uniqueaccess code comprising a returnable identification of the vehicularmobile terminal while the vehicular mobile terminal is within the cellcoverage of the macro base station; broadcasting uplink broadcastinformation including the unique access code to the plurality of microbase stations; and returning the unique access code to the macro basestation, in response to the vehicular mobile terminal decreasing inmobility.
 19. The method of claim 18, further comprising receivinginformation about a channel allocated for the unique access code fromthe macro base station, wherein the broadcasting of the uplink broadcastinformation comprises broadcasting the uplink broadcast informationusing the channel allocated for the unique access code.
 20. Acommunication method of a macro base station, the method comprising:identifying a mobility of a vehicular mobile terminal in a multi-cellgroup comprising the macro base station and a plurality of micro basestations within a cell coverage of the macro base station; allocating aunique access code and a channel for the unique access code to thevehicular mobile terminal based on the mobility of the vehicular mobileterminal, the unique access code comprising a returnable identificationof the vehicular mobile terminal while the vehicular mobile terminal iswithin the cell coverage of the macro base station; reporting about theunique access code and the channel for the unique access code to theplurality of micro base stations; and regaining the unique access codefrom the vehicular mobile terminal, in response to the vehicular mobileterminal decreasing in mobility.
 21. The method of claim 20, furthercomprising forwarding data about the vehicular mobile terminal from aserving micro base station to a neighbor micro base station based on arenewed data forwarding path, when a preparation level of a handoverassociated with a level of an operation used for the serving micro basestation and the neighbor micro base station to perform the handover usesdata forwarding.
 22. The method of claim 20, further comprisingforwarding data about the vehicular mobile terminal to a neighbor microbase station when a preparation level of a handover associated with alevel of an operation used for a serving micro base station and theneighbor micro base station to perform the handover uses cooperationbetween the serving micro base station and the neighbor micro basestation.
 23. A non-transitory computer-readable storage medium havingstored therein program instructions to cause a processor to implement acommunication method of a serving micro base station that is serving avehicular mobile terminal, the method comprising: identifying a uniqueaccess code allocated to the vehicular mobile terminal in a multi-cellgroup comprising a macro base station and a plurality of micro basestations that are within a cell coverage of the macro base station, theunique access code comprising a returnable identification of thevehicular mobile terminal while the vehicular mobile terminal is withinthe cell coverage of the macro base station; receiving uplink broadcastinformation including the unique access code from the vehicular mobileterminal; performing a handover of the vehicular mobile terminal basedon the uplink broadcast information; and regaining the unique accesscode from the vehicular mobile terminal, in response to the vehicularmobile terminal decreasing in mobility.
 24. The method of claim 1,wherein the regaining of the unique access code from the vehicularmobile terminal comprises regaining the unique access code in responseto the vehicular mobile terminal continuing to be moving but the speedat which the vehicular mobile terminal is moving decreases below apredetermined mobility.